Note: Descriptions are shown in the official language in which they were submitted.
WO 94/04709 PCT/AU93/00414
1 2137812
DPGRADING TITANIF»tOUS MATERIALS
This invention relates to the removal of impurities from
naturally occurring and synthetic titaniferous materials.
The invention is particularly suited to the enhancement of
titaniferous materials used in the production of titanium
metal and titanium dioxide pigments by means of industrial
chlorination systems.
Embodiments of the present invention have the common feature
of roasting of titaniferous materials in the presence of
additives a~ad at temperatures which encourage the formation
of a liquid oxide or glassy phase, followed at some stage by
cooling anct aqueous leaching as steps in an integrated
process. Additional steps may be employed as will be
described below..
In industrial chlorination processes titanium dioxide bearing
feedstocks are fed with coke to chlorinators of various
designs (fluidised bed, shaft, molten salt) , operated to a
maximum temp?erature in the range 700 - 1200C. The most common
type of industrial chlorinator is of the fluidised bed
design. Gaseous chlorine is passed through the titania and
carbon bearing charge, converting titanium dioxide to
titanium tel:rachloride gas, which is then removed in the exit
gas stream <<nd condensed to liquid titanium tetrachloride for
further purification and processing.
213~8~.2
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The chlorination process as conducted in industrial
chlorinators is well suited to the conversion of pure
titanium dioxide feedstocks to titanium tetrachloride.
However, most other inputs (i.e. impurities in feedstocks)
cause difficulties which greatly complicate either the
chlorination process itself or the subsequent stages of
condensation and purification and disposal of waste. The
attached table provides an indication of the types of
problems encountered. In addition, each unit of inputs which
does not enter products contributes substantially to the
generation of wastes for treatment and disposal. Some inputs
(e. g. particular metals, radioactives) result in waste
classifications which may require specialist disposal in
monitored repositories.
Preferred inputs to chlorination are therefore high grade
materials, with the mineral rutile (at 95-96% TiO,) the most
suitable of present feeds. Shortages of rutile have led to
the development of other feedstocks formed by upgrading
naturally occurring ilmenite (at 40-60% TiO,), such as
titaniferous slag (approximately 86% TiO,) and synthetic
rutile (variously 92-95% TiO,). These upgrading processes
have had iron removal as a primary focus, but have extended
to removal of magnesium, manganese and alkali earth
impurities, as well as some aluminium.
WO 94/04709 2~3,~8~2 ~ Pt'T/AU93/00414
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Elemental C:~lorinationCondensation Purification
Input
Fe, Mn C~~asumes Solid/liquid
chlorine, chlorides
cake, foul
increases ductwork,
gas volumes make sludges
Alkali & D~afluidise
alkali f:Luid beds
earth diae to
metals l:Lquia.
chlorides,
consume
chlorine,
coke
A1 Consumes Causes Causes
chlorine, corrosion corrosion,
coke makes sludges
Si Accumulates Can May require
in encourage distillation
chlorinator, duct from product
readucing blockage.
campaign Condenses
in
life. part with
Consumes titanium
coke, tetrachloride
chlorine
V Must be
removed, by
chemical
treatment and
distillation
Th, Ra Accumulates
in
chlorinator
brickwork,
radioactive;
causes
disposal
difficulties
In the prior art synthetic rutile has been formed from
titaniferouf; minerals, e.g. ilmenite, via various techniques.
According t:o t:he most commonly applied technique, as
variously operated in Western Australia, the titaniferous
~~.3'~$~.2
WO 94/04709 PCT/AU93/00414
4
mineral is reduced with coal or char in a rotary kiln, at
temperatures in excess of 1100 C. In this process the iron
content of the mineral is substantially metallised. Sulphur
additions are also made to convert manganese impurities
partially to sulphides. Following reduction the metallised
product is cooled, separated from associated char, and then
subjected to aqueous aeration for removal of virtually all
contained metallic iron as a separable fine iron oxide. The
titaniferous product of separation is treated with 2-5%
aqueous sulphuric acid for dissolution of manganese and some
residual iron. There is no substantial chemical removal of
alkali metals or alkaline earths, aluminium, silicon,
vanadium or radionuclides in this process as disclosed or
operated. Further, iron and manganese removal is incomplete.
Recent disclosures have provided a process which operates
reduction at lower temperatures and provides for hydrochloric
acid leaching after the aqueous aeration and iron oxide
separation steps. According to these disclosures the process
is effective in removing iron, manganese, alkali and alkaline
earth impurities, a substantial proportion of aluminium
inputs and some vanadium as well as thorium. The process may
be operated as a retrofit on existing kiln based
installations. However, the process is ineffective in full
vanadium removal and has little chemical impact on silicon.
In another prior art invention relatively high degrees of
removal of magnesium, manganese, iron and aluminium have been
achieved. In one such process ilmenite is first thermally
reduced to substantially complete reduction of its ferric
oxide content (i.e. without substantial metallisation),
normally in a rotary kiln. The cooled, reduced product is
then leached under 35 psi pressure at 140-150 C with excess
20% hydrochloric acid for removal of iron, magnesium,
WO 94/04709 2~3,~8~.2 PCT/AU93/00414
aluminium a.nd manganese. The leach liQuors are spray roasted
for regeneration of hydrogen chloride, which is recirculated
to the leac:hing~ step .
5 In other p~cocesses the ilmenite undergoes grain refinement
by thermal oxidation followed by thermal reduction (either
in a fluid:ised bed or a rotary kiln) . The cooled, reduced
product is ithen subjected to atmospheric leaching with excess
20% hydrochloric acid, for removal of the deleterious
impurities. Acid regeneration is also performed by spray
roasting in. this process.
In all of the above mentioned hydrochloric acid leaching
based processes impurity removal is similar. Vanadium,
aluminium and silicon:'removal is not fully effective.
In yet another process ilmenite is thermally reduced (without
metallisation) with carbon in a rotary kiln, followed by
cooling in a nun-oxidising atmosphere. The cooled, reduced
prbduct is leached under 20 - 30 psi gauge pressure at 130°C
with 10 - !i0% (typically 18 - 25%) sulphuric acid, in the
presence o1: a seed material which assists hydrolysis of
dissolved t:itania, and consequently assists leaching of
impurities. Hydrochloric acid usage in place of sulphuric
acid has been. claimed for this process. under such
circumstances similar impurity removal to that achieved with
other hydrochloric acid based systems is to be expected.
Where sulphuric acid is used radioactivity removal will not
be complete.
A commonly adopted method for upgrading of ilmenite to higher
grade products i.s to smelt ilmenite at temperatures in excess
of 1500°C with coke addition in an electric furnace,
producing .3 malten titaniferous slag (for casting and
WO 94/04709 ~13'7sa_.2 PCT/AU93/00414
6
crushing) and a pig iron product. Of the problem impurities
only iron is removed in this manner, and then only
incompletely as a result of compositional limitations of the
process.
In another process titaniferous ore is roasted with alkali
metal compounds, followed by leaching with a strong acid
other than sulphuric acid (Australian Patent No. AU-B-
70976/87). According to this disclosure substantial removal
of various impurities is achieved, with "substantial" defined
to mean greater than 10~. In the context of the present
invention such poor removal of impurities, especially of
thorium and uranium, would not represent an effective
process. No specific phase structure after roasting is
indicated for this process but it is evident from analytical
results provided (where product analyses, unlike feed
analyses do not sum to 100% and analyses for the alkali metal
added are not given) that there may have been significant
retention of the additive in the final product. Under the
conditions given it is herein disclosed that it is to be
expected that alkali ferric titanate compounds which are not
amenable to subsequent acid leaching will form. The
consequent retention of alkali will render the final product
unsuitable as a feedstock for the chloride pigment process.
In yet another process a titaaiferous ore is treated by
alternate leaching with an aqueous solution of alkali metal
compound and an aqueous solution of a mineral acid (US Patent
No. 5,085,837). The process is specifically limited to ores
and concentrates and does not contemplate prior processing
aimed at artificially altering phase structures.
Consequently the process requires the application of
excessive reagent and harsh processing conditions to be even
partially effective and is unlikely to be economically
WO 94/04709 PCT/AU93/00414
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7
implemented to produce a feedstock for the chloride pigment
process.
A wide range of potential feedstocks is available for
upgrading ~.o high titanic content materials suited to
chlorinatio:n. examples of primary titanic sources which
cannot be s~itisfactorily upgraded by prior art processes for
the purposes of production of a material suited to
chlorination include hard rock (non detrital) ilmenites,
siliceous leucoxeaes, many primary (unweathered) ilmenites
and large <inatase resources. Many such secondary sources
(e. g. titan:ia bearing slaQs) also exist.
Clearly there is a considerable incentive to discover methods
for upgrading of titaniferous materials which can
economically produce high grade products almost
irrespectively of the nature of the impurities in the feed.
The present invention provides a combination of processing
steps which may be incorporated into more general processes
for the upgrading of titaniferous materials, rendering such
processes a~Pplic:able to the treatment of a wider range of
feeds and producing higher quality products than would
otherwise bE~ achievable.
Accordingly,. the present invention provides a process for
upgrading a titaniferous material by removal of impurities
which procefas includes the steps of:-
(i) heating a titaniferous material to a
temperature less than 1300°C to produce a solid
ti.taniferous phase and a liquid oxide or glassy
phase in the presence of sufficient of
compounds which encourage the formation of the
liquid oxide or glassy phase;
WO 94/04709 PCT/AU93/00414
2i3'~~1
s
(ii) cooling the product of step (i) to form a
solidified material comprising the titaniferous
phase and an impurity bearing phase at a rate
sufficient to ensure the susceptibility of the
impurity bearing phase to leaching in either an
acid or alkaline leachant; and
(iii) leaching the solidified material in an acidic
or alkaline leachant to leach at least a
portion of the impurities.
In order to ensure the formation of the solid titaniferous
phase and the liquid oxide or glassy phase during the heating
step it will normally be necessary to add to the titaniferous
material, prior to the heating step, sufficient of a compound
that encourages the formation of the liquid oxide or glassy
phase. However, in some cases it will not be necessary since
the titaniferous material itself may contain sufficient of
such a compound.
It has been discovered that the process of the invention can
remove iron, magnesium and other alkaline earths, alkalis,
manganese, silica, phosphorus, alumina, vanadium, rare
earths, thorium and other radioactive elements, which
impurities form an almost comprehensive list of impurities
in titaniferous mineral sources. From most materials a
product purity of greater than 96% TiO, can be obtained.
Compounds added to the titaniferous material may be mixed
therewith by any means ranging from direct mixing of
additives prior to charging to thermal treatment to more
complex feed preparations such as the formation of
agglomerates or nodules of mixed products, to briquette
WO 94/04709 PCT/AU93/00414
213'~8~.2
9
production from feeds and additives. Many additives will be
effective. In particular it is herein disclosed that sodium,
potassium, lithium, phosphorus, silicon and boron compounds
and minerals (e. g. borax, trona and other alkali metal
carbonates,. spodumene, caustic soda) will be effective.
Additives may be incorporated individually or in combination
with other additives.
It is further disclosed herein that the formation of a glassy
phase by addition of alkali compounds can be achieved without
the formation of alkali titanate phases, reduced alkali
tita,nate pb.ases (e.g. NaTiO~ - compounds and solid solutions)
or alkali :Ferric titanate phases ( a . g . Na ( Fe, A1 ) 02 - Ti02
phases known as "bronses") in roasting. HThere such titanate
phases form their stability with respect to subsequent
leaching sleeps is such that the final product quality is
adversely affected. The incorporation of sufficient
quantities of further additives (e. g. boron or phosphorus
compounds) which substantially reduce alkali oxide chemical
activity ca.n have the effect of eliminating these phases.
Under many circumstances it will be beneficial to incorporate
multiple additives into the material to be treated by thermal
processing. Far example, it is herein disclosed that the
simultaneous presence of silica, anhydrous borax a.nd sodium
oxide in 101)0°C thermally processed material in weight ratios
of about 7 ::L :1 ensures the preferential formation of a glassy
phase over other phases containing silica or soda. In this
formulation the required borax addition is only just over 10°0
of the add:Ltion which would be required for an equivalent
amount of grlassy phase where other additives do not act as
extenders. Since borax is by far the most expensive additive
of the three additives in this case optimum economics are
achieved by the use of the extenders.
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WO 94/04709 PCT/AU93/00414
Thermal processing may be carried out in any suitable device .
The production of liquid phases would recommend rotary or
grate kilning, but shaft furnaces may also be used and it has
5 been found that fluidised beds can be used under some
circumstances. Any gaseous atmosphere conditions may be used,
from fully oxidising to strongly reducing. The thermal
processing atmosphere should be chosen to most suit other
steps in integrated processing. Reducing conditions may be
10 achieved Where desired by either the use of a sub
stoichiometric firing flame or the addition of coal, char or
coke with the thermal processing charge.
Thermal processing residence time at temperature will depend
on the nature of the additives and the feed, as well as the
operating temperature. Residence times of from 5 minutes to
five hours have been effective, allowing thermal processing
residence times to be set to most suit other requirements in
integrated processing.
The level of additive used and the conditions applied in
thermal processing should be such that glassy phase formation
does not exceed the limitations set by materials handling
constraints in the thermal processing step. For example,
where glassy phase formation exceeds about 15% by volume of
the roasted material it must be anticipated that accretion
and bed fusion problems will occur.
Cooling of the thermally treated material should be conducted
in such a manner as to limit the reversion of the glassy
phase to crystalline phases, i.e. should be at a sufficient
rate to a temperature at which the liquid glass solidifies as
to ensure the formation of at least a portion of solid glass
rather than complete formation of crystalline products.
X137812
'WO 94/04709 p~'t'/AU93/00414
11
Further, cooling should be conducted under an environment
appropriate to the conditions of thermal treatment (i.e.
reduction processing will require cooling in an oxygen free
environment;.
The aqueous; leaching step need not necessarily follow
directly after the presently disclosed thermal processing
step. For example if the thermal processing step is conducted
under oxidiF~inQ conditions it may be optionally followed by
a reduction step prior to aqueous leaching. Further,
crushinQ/Qri.adinQ of the thermally processed material to
enhance subf~equent leach performance may be undertaken.
The conditions necessary to conduct effective leaching will
depend on tb.e nature of the original feed and the additives.
For example,, addition of soda ash and borax to siliceous
leucoxene in accordance with the present disclosure will
result in a product which can be leached in sodium silicate
solution formed directly from the thermally treated material;
the active Leachant in this case is simply water. In other
cases up to 100 gpL caustic soda solution or acid will be an
effective leachant. Leaching will generally benefit
substantially by use of high temperature (e.g. 80°C or
above), although it has not been necessary to use pressure
leaching to achieve effective conditions. Nevertheless it is
presently disclosed that pressure leaching can be effectively
and success:Eully applied. Lower temperatures can also be
used, althov.gh with penalties in process kinetics.
Leaching ma;y be: conducted in any circuit configuration,
including batch single or multiple stage leaching, continuous
cocurrent mv~ltistage leaching, or continuous countercurrent
multistage leaching. For most circumstances two stage
cocurrent leaching will be most beneficial. Average residence
WO 94/04709 PCT/AU93/00414
2~.3"~8~.2 ,
12
time may vary from 30 minutes to 10 hours, depending on
process conditions. Any leach vessel capable of providing
adequate shear may be used. Simple stirred tank vessels are
applicable.
At the conclusion of leaching the leach liquor may be
separated from the mineral by any suitable means, including
thickening, filtration and washing. The mineral product may
then pass on to other steps in an integrated process . For
example, a further acid leach may follow the disclosed
leaching step, particularly where the titaniferous feed has
a content of alkalis or alkaline earths.
Other processing steps may be added as necessary or desired.
For example, reagent regeneration (e. Q. caustic regeneration,
hydrochloric acid regeneration, sulphuric acid regeneration)
can be used with the process in order to improve process
effectiveness or economics. Similarly, a physical separation
step may be employed at any stage (e. g. a final magnetic
separation to remove grains containing iron, such as
chromite).
Examples
Example 1
Sodium carbonate addition, corresponding to 4.25°o NazO by
weight, was made to a titania concentrate whose composition
is given in Table 1. The mixture was homogenised and
pelletised, and the pellets were heated in air to 1000°C for
4 hours. The thus roasted pellets were quenched in liquid
nitrogen and then crushed to pass a screen of 200 microns
aperture. The crushed roasted pellets were subjected to
leaching under reflux with 40 wt°o sodium silicate solution
(SiO~:Na20=2,4:1 by weight) at 4% slurry density. (Sodium
silicate solution was used to simulate leaching using water
WO 94/04709 ' ' ' PCT/AU93/00414
21.3'~B~.Z
13
as leachant: under conditions where the leach liquors are
recycled to leaching after solid/liquid separation).
Solid/liquid separation was effected by centrifuging, after
which the leach residue was washed and calcined at 1000°C for
analysis. ~~he analysis of the calcined product is also given
in Table 1.
The original concentrate was known to contain silica
primarily as quartz inclusions in titanate grains. X-ray
diffraction analysis after roasting indicated extinction of
all crystalline phases containing silica. A glassy phase
containing 16% Na,O, 46°~ SiO,, 9% A1,0" 26% TiO, and 3 % Fe,03
was identified in the roasted material by electron
microscopy. Sodium titanates and sodium iron titanium bronze
were also identified (along with rutile) by these techniques,
indicating ~~hat conditions were not optimised.
Nevertheles~a, highly effective concentrate upgrading has been
achieved evEan where the benefits of subsequent acid leaching
have not b~:en pursued, illustrating the benefits of the
formation c~f the glassy phase. Substantial removal of
silica, alumina and vanadium was achieved.
Example 2
This example illustrates the optimisation of additives for
both proces:a effectiveness and most economic formulation.
In this example titania concentrates of the composition given
in Table 2 mere used as titaniferous material for treatment.
Early work attempting to produce glassy phase with this
material by addition of sodium carbonate prior to roasting
indicated that glassy phase could easily be produced, but
over a wide range of conditions reduced sodium titanate or
WO 94/04709 PCT/AU93/00414
2i3'~8~..~
14
sodium iron titanate bronze formation which resulted in
sodium retention after leaching could not be easily avoided.
Complete and partial replacement of sodium carbonate by borax
was tested.
Two batches of hand pressed pellets were prepared as follows .
A 1008 sample of the concentrates (previously ground to
passing a screen aperture of 30 microns) was blended in each
case with 1.1% of the appropriate additive or additive
mixture and the resulting blends were pressed into pellets.
The first batch was prepared with 1.1 wt% of anhydrous borax
addition while the second batch was prepared with addition of
1.1 wt% of 1 . 1 Na,B,O,:Na,O.
Each batch of pellets was roasted for two hours in a 7 . 1
H,/CO, atmosphere at 1000°C and then removed to cool quickly
in the same atmosphere. The roasted pellets were ground to
pass a screen aperture of 75 microns for subsequent leaching.
Ground roasted pellets were caustic leached under reflux
conditions for 6 hours in a 10% NaOH solution at 6.7% solids
density. Solid/liquid separation was effected by filtration,
and the caustic leached products were washed and dried in
preparation for subsequent acid leaching.
The caustic leached residues were acid leached in 15°o HC1 for
4 hours under reflux, then similarly filtered, washed and
dried.
In each case samples of the concentrate and roasted material
were submitted for X-ray diffraction analysis. While quartz
and various ilmenite, anatase and rutile related phases were
identif ied in the concentrates the only crystalline phases
identified in the roasted product were rutile and ilmenite.
WO 94/04709 PCT/AU93/00414
213"78~.~
All quartz had entered a glassy phase, and no titanate phases
which would reduce leach effectiveness were identified.
Analyses of the caustic and acid leach residues in each case,
5 illustratinST the effectiveness of the process where optimum
conditions nre applied, are provided in Table 3.
Example 3
The same pellet formulations as indicated in Example 2 were
10 made up in 350 kg batches in an agglomeration plant and
roasted at 30 kg/hr feed rate with 15°~ brown coal char
addition to a final temperature of 1000°C in a small (0.5m
diameter) rotary kiln. Residence time above 900°C was
approximate7.y 10 minutes. There were no problems with
15 accretions or bed fusion, and after separation from residual
char the products had exactly the same properties as the
roasted products of Example 2.
Example 4
A caommercia;l titania slag product having the composition
indicated in Table 4 was processed as for the processing
conditions indicated in Example 2, but with 2 wt% anhydrous
borax addition in place of the other additives. The caustic
leach was conducted at 165°C under pressure, and a pressure
leach with 20°s sulphuric acid conducted at 135°C was used in
place of the hydrochloric acid leach. The final residue was
calcined at 9001°C for one hour. The products of this
treatment are indicated in Table 4.
Example 5
This example when compared with examples 1 and 2 illustrates
the advantages of the formation of a glassy phase.
Concentrates having the composition indicated in Table 1 were
WO 94/04709 ~''~3~~ iC; PCT/AU93/00414
16
subjected leaching under atmospheric reflux conditions With
excess 20% HCl. After separation of the residue from the
liquor followed by washing and drying of the residue its
composition was as given in Table 5. Clearly there was
ineffective removal of virtually all impurities of interest
by comparison with the other examples provided herein.
Table 1: Concentrates and Product from Example 1
wt% Concentrate Product
Ti02 85.8 94.9
Fe203 2.25 1.91
A1203 1. 08 0 . 63
Si02 7.62 0.74
Nb205 0 . 3 0 0 . 31
V2O5 0.235 0.02
Na20 0.0 1.10
Table 2: Composition of Concentrates
Used in Examples 2 and 3
wt~
0
Ti02 63 . 6
Fe203 28 . 6
Si02 3.53
A1203 0 . 80
Mg0 0.87
Ca0 0.02
Cr203 0 . 55
Mn0 1.11
3 0 V205 0 . 22
Zr02 0 . 2 6
P205 0.04
U30e 0 . 002
Th02 0 . 01
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17
Table 3: Compositions of Leach Products from Example 2
1. ~~ % 1.1 % 1:1 Na2B40~ : Na20
NazB40~
additio n addition
wt% CauF~tic Acid Leach Caustic Acid Leach
Leach Residue Leach Residue
Res i.due Res idue
Ti02 66 . !~ 94 . 3 67 . 3 94 . 9
F'e203 27.1 30.2 30.6 2.04
SiO~ 1. ~~2 0 . 99 0 . 55 0 . 86
A1203 0.::2 0.17 0.14 0.15
Mg0 0.97 0.08 0.90 0.09
Ca0 0.05 0.001 0.03 0.001
Cr203 0 . E.8 0 . 69 0 .70 0 . 67
Ma0 1.1.5 0.06 1.19 0.06
V205 0.2.2 0.15 0.23 0.13
ZrOz 0.27 0.37 0.28 0.38
Na20 0.05 0.02 0.15 0.03
P205 0.02 0.02 0.01 0.02
U3O8 0.002 0.002 0.002 0.002
Th02 0.01 0.003 0.01 0.004
2t3'~8~.2. PCT/AU93/00414
WO 94/04709
18
Table 4: Feed and Product in Example 4
wto Commercial Roast/Leach
Slag Product
Ti02 79.7 97.2
Fe0 9.24 0.85
Si02 3.11 0.09
A1~03 3 . 23 0 . 38
Mg0 4.81 0.43
Ca0 0.41 0.002
Cr203 0 .16 0 .12
Mn0 0.25 0.02
VZOS 0.57 0.12
ZrOa 0.046 0.06
PZOS 0.002 0.004
U308 0.0005 n.d.
ThOa 0.0006 n.d.
n.d. - not determined
Table 5: Results of Processing as described in Example 5
wt% Leach Product
Ti02 88 . 6
Fe203 0.98
Si02 7 . 54
A1203 0 . 6 5
V205 0 .198
U308 0.0054
Th02 0.0094
